Waste reduction systems have been in use for many years. A typical system includes a pulper unit, such as the SP-75S pulper manufactured by the Somat.RTM. Corporation of Coatesville, Pa., and a liquid extraction unit, such as the HE-6S Hydra Extractor.RTM. unit produced by the same manufacturer.
In a typical pulper system, kitchen waste is placed into a large cylindrical tank that is partially filled with water. A cutting mechanism is typically installed at the bottom of the tank. The cutting mechanism includes a rotating impeller plate with rotating blades that periodically come into play with stationary blades. The rotation of the impeller grinds the waste into a pulp and circulates the water in the tank. Waste particles that are sufficiently small are discharged from the tank and are passed through a conduit to the liquid extraction assembly.
The extraction assembly typically includes a vertical or near vertical feed screw surrounded by a cylindrical screen. The screw rotates at a speed between 85 and 90 revolutions per minute, to advance the solid particles within the pulp vertically towards the top of the extractor. The water within the pulp drains out through the screen due to gravity, and is returned for re-use in the tank. Some systems have included inverted conical restrictor elements at the top (discharge) end, to compress the solid material before discharge for additional liquid removal. The partially dried material at the top of the feed screw is then removed for disposal.
The waste reduction systems developed in the prior art occupy a large footprint and the extractor is typically very tall, often 2 meters in height. The prior art waste handling systems also have been expensive to manufacture (and purchase). Installation often requires technicians to install lengthy conduits between the pulper unit and the extractor unit; the costs for the complex installation often run between 15% and 25% of the purchase cost. In order to improve the footprint, some "close coupled" systems have been developed. These systems have a relatively short distance (e.g., about 30 centimeters) between the pulper and the extractor.
After installation, the prior art systems typically require frequent maintenance by trained personnel after installation. The need for maintenance is particularly acute in two areas of the system: the impeller and the liquid extraction apparatus. Impeller blades have been prone to damage when non-pulpable objects (e.g., metal flatware) become lodged in the blades. Some systems have included replaceable blades, but the blade replacement is a delicate operation requiring a skilled technician. The extractor unit also requires relatively frequent maintenance, to ensure that particles do not clog the openings in the screen or become hardened on the flighting of the screw. Removing the screw and screen is a complex operation also requiring a technician.
The large space requirement and operating costs have typically limited the use of these waste reduction systems to large institutions, such as hospitals, large hotels and cruise ships. The systems have generally not been practical for small institutions (e.g., restaurants) that generate the same types of waste as the large institutions, albeit in smaller quantities. In order to make waste reduction systems available to a greater variety of users, many design changes are required. At the same time that it is desirable to make the unit smaller, it is also desired to improve the accessibility of parts that must be cleaned or serviced. It is desirable to simplify maintenance, so that individuals with comparatively little training can maintain the machine.